#include <iostream>
#include <algorithm>
using namespace std;
struct node
{
	int p,s;
	double q;
}arr[100001];

bool biger(const node& a,const node& b)
{
	return a.q > b.q;
}
int main()
{
	int n,k;
	ios::sync_with_stdio(false);
	cin >> n >> k;
	for(int i = 0 ; i < n ;++i)
	{
		cin >> arr[i].s >> arr[i].p;
		arr[i].q = (double(arr[i].s))/(double(arr[i].p));
	}
	sort(arr,arr + n,biger);
	int sum_p = 0,sum_s = 0;
	for(int i = 0 ; i < k ;++i)
	{
		sum_p += arr[i].p;
		sum_s += arr[i].s;
	}
	cout.precision(3);
	cout << fixed << double(sum_s)*100 / sum_p  << endl;
}
